I. Field of the Invention
This invention relates to a process for the preparation of catalysts from molybdenum polysulfide precursors, and to the use of such catalysts in hydrotreating. In particular, it relates to a process for the preparation of species of highly active, highly selective, hydrotreating catalysts from molybdenum polysulfide catalyst precursors characterized as ammonium, or substituted ammonium trimolybdenum polysulfide trimers, and the use of such catalysts in hydrotreating processes.
II. Background and Prior Art
Hydrotreating processes are basic, and very well known to the petroleum refining industry. These processes require the treating with hydrogen of various hydrocarbon fractions, or whole heavy feeds, or feedstocks, in the presence of hydrogenation (hydrogen transfer) catalysts to effect conversion of at least a portion of the feeds, or feedstocks to lower molecular weight hydrocarbons, or to effect the removal of unwanted components, or compounds, or their conversion to innocuous or less undesirable compounds. Hydrotreating may be applied to a variety of feedstocks, e.g., solvents, light, middle, or heavy distillate feeds and residual feeds, or fuels. In hydrofining relatively light feeds, the feeds are treated with hydrogen, often to improve odor, color, stability, combustion characteristics, and the like. Unsaturated hydrocarbons are hydrogenated, and saturated. Sulfur and nitrogen are removed in such treatments. In the treatment of catalytic cracking feedstocks, the cracking quality of the feedstock is improved by the hydrogenation. Carbon yield is reduced, and gasoline yield is generally increased. In the hydrodesulfurization of heavier feedstocks, or residuas, the sulfur compounds are hydrogenated, and cracked. Carbon-sulfur bonds are broken, and the sulfur for the most part is converted to hydrogen sulfide which is removed as a gas from the process. Hydrodenitrogenation, to some degree also generally accompanies hydrodesulfurization reactions. In the hydrodenitrogenation of heavier feedstocks, or residuas, the nitrogen compounds are hydrogenated and cracked. Carbon-nitrogen bonds are broken, and the nitrogen is converted to ammonia and evolved from the process. Hydrodesulfurization, to some degree also generally accompanies hydrodenitrogenation reactions. In the hydrodesulfurization of relatively heavy feedstocks, emphasis is on the removal of sulfur from the feedstock which is usually converted to lower molecular weight, or lower boiling components. In the hydrodenitrogenation of relatively heavy feedstocks emphasis is on the removal of nitrogen from the feedstock, which also is converted to lower molecular weight, or lower boiling components. Albeit, hydrodesulfurization and hydrodenitrogenation reactions generally occur together, it is usually far more difficult to achieve effective hydrodenitrogenation of feedstocks than hydrodesulfurization of feedstocks.
The dwindling supplies of high grade petroleum feedstocks necessitates the increased production and processing of transportation fuels from lower grade, heavy petroleum feedstocks and synthetic liquid hydrocarbons derived from hydrocarbon-containing, or precursor hydrocarbon-containing, solids. The refiners feedstock sources as a result thereof continues to change, particularly as the worldwide supplies of petroleum diminish. The newer feedstocks often contain higher amounts of nitrogen, sulfur, and other materials. Nonetheless, whatever the difficulties, it remains a necessity to effectively hydrotreat the new feedstocks; often to a greater extent than previously was required. It has thus become necessary to process whole heavy petroleum crudes and residua from unconventional sources, as well as synthetic fuels (syncrudes; e.g., liquified coal, or coal from coal carbonization, oil from tar sands, shale oil and the like inclusive of residua or viscous syncrude fractions). All, particularly the later, are under active consideration as commercial feedstocks, or feedstock replacements for higher grade petroleum sources. Feedstocks derived from these sources are often of high olefinic content, contain more sulfur or nitrogen, or both, than feedstocks derived from more conventional crude oils.
Naphthas, notably those derived from syncrudes, viz., residua, shale oil, and coal, are highly unsaturated and contain considerably more sulfur, nitrogen, olefins, and condensed ring compounds than the more conventional naphthas. For example, nitrogen and sulfur are contained in cat naphtha in concentrations ranging upwardly from 50 ppm and 1000 ppm, respectively. In coal liquids nitrogen and sulfur are present in concentrations ranging upwardly from 1300 ppm and 5000 ppm, respectively; and oxygen is present in even higher concentrations. These compounds cause activity suppression and an all too rapid deactivation of the catalysts. Coke formation is increased, and there is more cracking with increased gas production. Albeit these compounds, except for condensed ring naphthenic compounds, can be removed by conventional hydrofining, this is a severe, if not an intolerable process burden due to the large hydrogen consumption; and hydrogen becomes more and more a very expensive commodity. Thus, generally considerably more upgrading is required to obtain usable products from these sources. Such upgrading generally necessitates hydrotreating the various hydrocarbon fractions, or whole crudes, and includes reactions such as hydrogenating to saturate olefins and aromatics, hydrodesulfurizing to remove sulfur compounds, hydrodenitrogenating to remove nitrogen, and conversion of high boiling compounds to lower boiling compounds.
Typical hydrotreating catalysts are exemplified by sulfided cobalt molybdate on alumina, nickel molybdate on alumina, cobalt molybdate promoted with nickel, and the like. Certain transition metal sulfides such as cobalt and molybdenum sulfides and mixtures thereof have also been employed in hydrofining processes for upgrading oils which contain sulfur and nitrogen compounds. For example, U.S. Pat. No. 2,914,462 discloses the use of molybdenum sulfide for hydrodesulfurizing gas oil and U.S. Pat. No. 3,148,135 discloses the use of molybdenum sulfide for hydrorefining sulfur and nitrogen-containing hydrocarbon oil. U.S. Pat. No. 2,715,603 discloses the use of molybdenum sulfide as a catalyst for the hydrogenation of heavy oils, while U.S. Pat. No. 3,704,783 discloses the use of molybdenum sulfides for producing sulfur-free hydrogen and carbon dioxide, wherein the molybdenum sulfide converts carbonyl sulfide to hydrogen sulfide. A serious disadvantage associated with the use of such catalysts is their relatively high cost, and the supply of catalytic metals is rather limited. Moreover, the reaction rates of such catalysts are relatively slow, particularly in the presence of nitrogen; and hydrogen consumption is quite high. These latter problems are particularly oppressive when it is realized that new generation feeds are unusually high in nitrogen, or sulfur, or both, and the cost of hydrogen is increasing at very high rates.
Molybdenum sulfide is also known to be useful for water gas shift and methanation reactions, as well as for catalyzed hydrotreating operations. Recently, e.g., it was disclosed in U.S. Pat. Nos. 4,243,553 and 4,243,554 that molybdenum disulfide catalysts of relatively high surface area can be obtained by thermally decomposing selected thiomolybdate salts at temperatures ranging from 300.degree.-800.degree. C. in the presence of essentially inert, oxygen-free atmospheres, e.g., atmospheres of reduced pressure, or atmospheres consisting of argon, nitrogen, and hydrogen, or mixtures thereof. In accordance with the former, a substituted ammonium thiomolybdate salt is thermally decomposed at a very slow heating rate of from about, 0.5.degree. to 2.degree. C./min and in accordance with the latter an ammonium thiomolybdate salt is decomposed at a rate in excess of 15.degree. C. per minute to form the high surface area molybdenum disulfide.
III. Our application Ser. No. 399,947
In our application Ser. No. 399,947, filed July 20, 1982, supra, there is disclosed a process for the preparation of hydrotreating catalysts formed from a catalyst precursor comprising an ammonium, or substituted ammonium tri-molybdenum polysulfide complex salt, or molybdenum trimer, which is contacted with a hydrocarbon feedstock, or hydrocarbons, and decomposed, in the presence of hydrogen, and sulfur, or sulfur-bearing compound. The catalyst precursor, when decomposed in the presence of hydrogen, and hydrocarbon and sulfur, forms a reaction product which is a highly active, selective and stable hydrotreating catalyst.
The catalyst precursor, i.e., the ammonium, or substituted ammonium tri-molybdenum polysulfide complex salt, or molybdenum trimer, as disclosed in said application, is characterized by the formula EQU B.sub.x [Mo.sub.3 S.sub.z ]
where B is an ammonium ion, polyammonium ion, or tertiary or quaternary phosphonium ion, or an organo or hydrocarbyl substituted ammonium ion (e.g., a primary, secondary, tertiary or quaternary substituted ammonium ion), organo or hydrocarbyl substituted polyammonium ion, or an organo or hydrocarbyl substituted tertiary or quaternary phosphonium ion, x is 1 where B is a divalent cationic moiety, or 2 where B is a monovalent cationic moiety, and [Mo.sub.3 S.sub.z ] is a divalent anionic moiety wherein z is an integer ranging from about 10 to about 46, preferably from about 12 to about 20.
These precursor catalyst species can be unsupported, or supported as where distended or dispersed upon a porous, refractory inorganic oxide carrier. In forming a supported precursor catalyst species, the trimer is formed in situ upon the support, or the trimer, after its formation, is dispersed or dissolved in a solvent and incorporated with a preselected quantity of said porous, refractory inorganic oxide support, preferably a particulate mass of said support, and the trimer-containing support then preferably dried without decomposition of said trimer, to remove all or a portion of the solvent from the support. Generally, sufficient trimer is incorporated on the support to provide from about 3 percent to about 20 percent, preferably from about 6 percent to about 17 percent of molybdenum as trimer, expressed as weight percent Mo on an ignition loss free basis. In completing formation of a catalyst the dried particulate mass containing the precursor catalyst species is contacted and decomposed in the presence of hydrogen with a hydrocarbon, and sulfur or a sulfur-bearing compound; or contacted and decomposed in the presence of hydrogen with a compound which supplies both the hydrocarbon and sulfur species, i.e., a sulfur-containing hydrocarbon compound, e.g., a heterocyclic sulfur containing compound, or compounds. In conducting a hydrotreating reaction, a hydrocarbon feedstock and hydrogen are contacted with the catalyst at hydrotreating conditions.
In the application it was disclosed that highly active catalysts could be formed from the catalyst precursor when the amount of sulfur associated with the molybdenum of the [Mo.sub.3 S.sub.z ] moiety appeared less than was required to satisfy the valence of the molybdenum, or greater than that which was required to satisfy the valence of the molybdenum. The preferred values of "z" in the formula B.sub.x [Mo.sub.3 S.sub.z ], supra, ranged from about 12 to 20, though values ranging from about 10 to 46 were suggested as acceptable. In the preparation of the B.sub.x [Mo.sub.3 S.sub.z ] catalytic precursors, however, the consistency, and reproducability of the data has been less than desirable. Thus, though it had been recognized that the more active catalysts were formed from the B.sub.x [Mo.sub.3 S.sub.z ] catalytic precursors wherein z ranged from about 12 to 20, it proved rather difficult to consistently, and reproducibly prepare these preferred species of catalyst precursor. Oddly enough also, even when catalysts were prepared from the B.sub.x [Mo.sub.3 S.sub.z ] catalyst precursors where the z value ranged from about 12 to 20, sometimes even these catalysts were not as active as would otherwise have been expected. It was also found that the activity of the catalyst prepared from a B.sub.x [Mo.sub.3 S.sub.z ] catalyst precursor was affected by the amount of carbon formed in the catalyst produced from a catalyst precursor. The presence of high carbon levels in the finished catalyst has been found to adversely affect catalyst aromatics hydrogenation and hydrodenitrogenation activity, and catalysts which have an atomic ratio of C/Mo above about 0.05 have been found to be less active than desired.
IV. Objects
It is, accordingly, the primary object of the present invention to obviate these and other disadvantages.
A particular object of this invention is to provide a novel process for the preparation of B.sub.x [Mo.sub.3 S.sub.z ] catalyst precursors from which highly active catalysts can be consistently and reproducibly prepared.
A further, and more specific object is to provide a novel process for the more consistent and reproducible preparation of a preferred class of B.sub.x [Mo.sub.3 S.sub.z ] catalyst precursors; from which more highly active catalysts can be consistently and reproducibly prepared.
It is also an object to provide more highly acitive hydrogenation catalysts, as well as a novel process for this preparation, and use.